what is wrong with my x-rite 810 densitometer?

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I just got my x-rite 810 densitometer. After I pluged in and turn power on, the screen desplay "PWR DWN V2B05". No matter which key I pushed it did not react. what is wrong with this unit? I checked x-rite website and did not find useful information for this problem, menu did not mention this error too. In another thread someone mentioned changing battery inside of unit. I did open the back cover of unit and no clue about which is the battery. Could someone show me a picture that indicates where the battery locates? Or tell me how to fix this problem.